The invention relates to a vacuum gripping apparatus for moving roll-like loads, the loads being piled on top of each other and resting on their even end faces and the vacuum gripping apparatus comprising a suction plate to be arranged against the end face of a load.
The described vacuum gripping apparatus can be used for lifting and moving rolls of reeled paper, metal, plastic or laminate, for example. It can also be used for moving cylindrical hollow pieces having even end faces. The vacuum gripping apparatus can be liftably and lowerably suspended to a lifting device of a crane, although other lifting apparatuses can also be used.
A conventional prior art vacuum gripping apparatus is described in publication DE-U 84 35 161. The apparatus comprises an even suction plate in the lower portion, with several concentric ring seals arranged at a distance onto the underside of the suction plate to provide the gripping surface. When the suction plate is placed down onto the end face providing the gripping surface of the load, the ring seals form vacuum spaces, separated from one another, between the suction plate and the load to be transported. Naturally the ring seals do not have to be circular but they may have any other form, too; they may be elliptical or angular, for example, as long as they form a closed ring. It is not absolutely necessary that the ring seals are within each other either. It is also possible to arrange several vacuum spaces formed at a distance from one another.
The vacuum spaces are connected through holes provided in the suction plate and a connecting conduit comprising a valve to a vacuum source comprising a vacuum generator. When there is no load suspended from the vacuum gripping apparatus, the connection to the suction generator is cut off and the vacuum space or spaces are ventilated.
To lift a load, the vacuum gripping apparatus is lowered onto the load and the valve device is set in a suction position, thereby creating a connection between the vacuum source and the vacuum space or spaces. If several vacuum spaces are used, several valves can also be arranged, the valves being arranged in such a way that the connection to the vacuum source opens only when the vacuum space in question is fully covered by the load gripping surface. When the vacuum space or spaces have been subjected to a sufficient vacuum in the lifting process, the load can be lifted or moved.
After the load has been lifted or deposited, the valve device is switched from the suction position back to the ventilation position. The vacuum gripping apparatus can then be lifted with the lifting device from the lowered load.
The above described vacuum gripping apparatus comprises a vacuum container above the suction plate, the container and the suction plate both having a circular horizontal cross-sectional form. The upper surface of the container provides a mounting surface for arranging various kinds of aggregates and devices that are necessary for the use of a vacuum lifting apparatus.
Roll stacks can be more than 12 m high, so due to reasons of space, they must be arranged extremely close to each other. For roll diameters up to 2500 mm, the minimum free distance between two roll stacks can be 100 mm, for example. To prevent the vacuum gripping apparatus from colliding with the roll stacks when the apparatus is driven into a cavity surrounded by the roll stacks, the apparatus may not be greater than the maximum diameter of the roll to be received.
Various solutions have been presented to solve the problems of space thus arising in the mounting of the aggregates and other devices needed in the vacuum gripping apparatus. It has been suggested that separate aggregates would be removed from the vacuum gripping apparatus and arranged to the lifting apparatus. On the other hand, FI Patent 94615 proposes that the mounting space in question would be formed into a hexagon, as this would allow optimal use of the space between the roll stacks without increasing the risk of collision with the roll stacks, thereby providing more mounting space for the aggregates.
If it is necessary to store rolls of clearly different diameters (two different diameters, for example) into one and the same storage area, the most reasonable way to utilize the space is to store the rolls in a matrix format according to size. Current technology requires that the diameter of the vacuum gripping apparatus, and that of the suction plate in particular, must be selected according to the smaller (or the smallest) matrix. Depending on the weight of a roll, sufficient suction power ensuring safe lifting of rolls of a greater diameter cannot always be provided. On the other hand, a small suction diameter is not enough to support the end surface of looser rolls, and the form of the rolls cannot be maintained during the lifting.
An object of the present invention is to solve the last one of the above problems. The object is achieved with a vacuum gripping apparatus according to the invention, characterized in that the outer circumference of the suction plate is provided with corner portions, the side edges connecting the corners of the portions being curved inward, and that the outer circumference of the suction plate determines the maximum lateral dimensions of the structure above the suction plate.
The invention, particularly as regards the suction plate, is based on the fact that the minimum distance between a roll stack and the surrounding roll stacks is always at one point only, i.e. on the lines connecting the centers of the roll stacks. Between the connecting lines the distance is longer, free surfaces being thus formed. The invention is based on the idea of utilizing the surface areas, in the suction plate in particular, without increasing the risk of collision with adjacent roll stacks. The only restriction on the upper structure is that it is not to extend beyond the edges of the suction plate in lateral direction. The upper structure can thus be a prior art structure, for example, or like the one presented in the solution of the above mentioned FI Patent. The most essential objective is therefore to increase suction power by maximizing the surface of the suction plate.
To optimally utilize the space between the roll stacks, the number and form of the corner portions in the suction plate can be adjusted according to a particular arrangement of roll stacks in storage.
Most commonly, in modern storage areas, roll stacks are arranged in such a way that the centers of the roll stacks form the corners of equilateral triangles. The appropriate form for the outer circumference of the suction plate of the invention is a regular polygon, preferably a hexagon. In other roll stack arrangements, different polygons optimally utilizing the available space are naturally possible.
A particularly large increase in surface is obtained by curving inward the side edges connecting the corners of the corner portions, most preferably into an arch form. In concrete applications this is appropriately achieved when the arch-formed side edges are concentric with adjacent roll stacks in such a way the side edges are at their entire length at the allowed minimum distance from the adjacent roll stacks, the free space thus being optimally used. To avoid sharp-edged corners, the edges should preferably be bevelled.
To allow the obtained increase in suction plate surface to provide a maximum increase in suction force, the outermost seal edge of the seal arrangement on the underside of the suction plate should follow the form of the outer circumference of the suction plate as close to the edge of the outer circumference as possible.